While it tends to be the larger ISP's I have had problems with, I do not rember having to deal with AT&T. Mostly CS, and another I can not seem to remember at the moment. The weirdest ISP that was blocking us was a Russian ISP. The language barrier made dealing with them kind of interesting. Thanks for sending them an email. It means more to them when a person who is actually paying them sends them an email.
When you hear back, if you could please let me know their response.
Jason